ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Spectrophotometric determination of ethacizine in tablets via oxidative conversion to its sulfone

Olena Mozgova, Liubomyr Kryskiw, Tetyana Kucher, Mykola Blazheyevskiy, and Valeriy Moroz

Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland

E-mail: omozgova@ichf.edu.pl

Received: 20 November 2025  Accepted: 13 March 2026

Abstract:

Ethacizine (ETC, syn. ethacyzine) is a Class IC antiarrhythmic agent and a new drug for the treatment of severe and/or refractory ventricular and supraventricular arrhythmias. The main goal of this paper consisted in the optimization and development for a novel, simple, selective, rapid, and cost-effective UV-spectrophotometric quantitative analysis method of ETC in pure solutions and tablet formulations. The method was based on the preliminary oxidation of the sulfur atom in the phenothiazine ring to the sulfone (λ_max = 328 nm, ε = 4553 dm³/mol cm) using KHSO_5, followed by absorbance measurement at 328 nm. Under optimal conditions (c(KHSO₅) = 6 × 10^–4 mol/dm³, pH = 8.1) good linearity was obtained in the range of 5–100 μg/cm³ of ETC with a correlation coefficient of 0.9999: A = (0.0101 ± 0.00005) × c [μg/cm³] + (0.01 ± 0.003) and the quantification limit, LOQ (10 s) was 2.95 μg/cm³. The high sensitivity of this method was accompanied by very good reproducibility. The precision of the method was evaluated by analyzing ETC solutions in five replicates at three levels (20.0, 40.00 and 60.0 µg/cm³). The mean recoveries ranged from 101.0 to 101.7%, with standard deviations ranging from 1.6 to 2.1%. During ETC determination in 50 mg tablets produced by “OlainFarm” (Latvia), the RSD was 1.6%; |δ|< t_α (0.95, n = 7) × RSD/√n is satisfied, indicating that there is no systematic error, and therefore the analysis results are correct (δ = (\(\overline{x }-\)µ) × 100/µ; µ is the content stated in the certificate). Thus, proposed method can be successfully applied in rapid routine quantification of ETC in pharmaceutical quality control laboratories for pure substances and tablet forms. In addition, the developed methodology adheres to the principles of green analytical chemistry as it does not require the use of hazardous reagents.

Keywords: Ethacyzine; UV-spectrophotometry; Indirect method development; Potassium hydrogen peroxomonosulfate; Oxone; Green chemistry

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04811-8

Chemical Papers 80 (6) 6995–7003 (2026)